Microscopic imaging of an object to be investigated with direct optical sectioning can be obtained with a plurality of confocal microscopy techniques. All known confocal microscopy techniques use point or pattern scanning systems with conjugate pairs of illumination and detection apertures for collecting light generated in response to an illumination in a focal plane within the object. Scanning systems using spatial light modulators like a micro-mirror device (or: “DMD”, digital mirror device) provide a plurality of advantages in terms of data acquisition speed, spatial resolution and optical efficiency. The DMD provides an illumination of the object with a pattern sequence of illumination spots focused to conjugate locations in the focal plane of the object while simultaneously collecting detection light from the conjugate locations with a detector camera (see e.g. EP 911 667 A1 and EP 916 981 A1).
An example of a conventional spatially light modulated imaging system for confocal imaging an object 1′ is schematically illustrated in FIG. 7 (prior art, see FIG. 3 of EP 911 667 A1). The conventional programmable confocal microscope 200′ comprises a light source device 210′, an imaging optic 220′, a detector device 230′ including two detector cameras 231′, 232′ and an optical modulator device 100′, which is arranged for directing illumination light from the light source device 210′ to the object 1′ and for relaying detection light from the object 1′ to the detector device 230′. To this end, the optical modulator device 100′ includes a micro-mirror device 110′ and first and second optical relaying devices 120′, 130′.
The micro-mirror device 110′ comprises an array of mirror elements 111′, which can be tilted between two different tilting states resulting in first and second tilting angles relative to a normal of the micro-mirror device 110′. In the first tilting state 111a′, the mirror elements 111′ create illumination spots focused at conjugate locations in the object 1′ and direct detection light from conjugate locations (conjugate image) via the first optical relaying device 120′ to the first detector camera 231′. Simultaneously, the remaining mirror elements 111′ in the second tilting state 111b′ collect detection light from non-conjugate locations (non-conjugate image) in the object 1′, which is directed via the second optical relaying device 130′ to the second detector camera 232′. Both of the conjugate and non-conjugate images collected with the first and second detector cameras 231′, 232′ are used for obtaining a optically sectioned image of the object 1′.
The first and second optical relaying devices 120′, 130′ each consist of a plane mirror, which relays the detection light from the mirror elements 111′ in the first (111a′) and second (111b′) states to optical axes 121′, 131′, resp. The optical axes 121′, 131′ are parallel to each other and to the axis from the imaging optic 220′ to the micro-mirror device 110′. Due to the tilting of the mirror elements 111′, the images from the conjugate locations and non-conjugate locations in the object 1′ are not perpendicular but tilted relative to the optical axes 121′, 131′. For preserving the image focus across the image, the detector cameras 231′, 232′ are rotated (tilted) relative to the optical axes 121′, 131′.
The conventional optical design with rotated detector cameras results in a plurality of disadvantages, which may restrict the quality of confocal microscopic images. Firstly, due to the slanted incidence, directing the conjugate and non-conjugate images onto rotated detector cameras results in trapezoidal distortions (“keystoning”) as well as increased reflection losses. This may represent a problem in particular with regard to the conjugate image inherently having a low intensity. Furthermore, the effective area of the detector camera is reduced due to the projection on the tilted detector camera. A further disadvantage may result from the fact that the conventional technique requires the provision of two separate detector cameras. Imaging both conjugate and non-conjugate images on a common detector camera would require complex optical elements, which again would reduce the light intensity. Using separate detector cameras may have disadvantages in terms of calibrating different sensitivities and resolutions relative to each other and rendering the system more expensive and complex.
The above disadvantages do not only occur with the example of FIG. 7 (prior art), but also with all other optical designs of conventional programmable confocal microscopes with micro-mirror devices as well as with other applications of micro-mirror devices, like e.g. for depletion microscopy methods.